The present invention relates to motorized servo-actuators and particularly servo-actuators employing a small subfractional horsepower electric motor driving a speed reducer or gear train for providing a mechanical movement or force output for performing a desired load function. Electric servo-actuators of this type find application in engine-driven vehicles where it is desired to provide electrical control of the vehicle engine throttle. Such electrical engine throttle control is desirable for vehicles equipped with an automatic cruise control function or a traction control mode of operation for the power train. In the vehicle cruise control function, the throttle position is electrically regulated about a desired set speed to provide substantially constant vehicle speed. In the traction control mode of operation, the vehicle throttle is modulated to prevent loss of wheel traction despite mechanical movement of the accelerator pedal by the vehicle operator. The servo-actuator thus intervenes in the throttle control to maintain excess driving force to the wheel in a manner not to cause loss of traction.
Where electric engine throttle actuators have been employed for cruise control and traction control modes of operation, it has been desired to provide for instantaneous and disablement of the electric throttle actuator for providing emergency throttle release in the event of a malfunction in the control of the servo motor. Typically, the electrical servo-actuator is connected to the throttle shaft by means of an electrically operated clutching mechanism to permit total mechanical disengagement of the electric servo-actuator from the vehicle throttle. In the event of mechanical malfunction upon electrical de-energization of the clutching mechanism, it has been desired to provide for positive force disengagement of the clutching mechanism.